1. Field of the Invention
The present invention relates to a lamp holder for a lamp with a single base, and especially relates to a bayonet-type lamp holder for a high brightness and large-scale size of a lamp such as a fluorescent lamp with a single base.
2. Description of the Related Art
In recent years, the high output and large-scale size of a fluorescent lamp having a single base is used as a substitute light source of an HID lamp, and it is necessary therefore to be able to improve certainty of lamp holding.
In the conventional HID lamp generally, screw-type base and lamp holder are used, so that the HID lamp is turned a lot when it is mounted on a lamp holder. Thus, there was very little possibility that the lamp fell to even if clamping of the lamp was a little loose.
On the other hand, a fluorescent lamp with a single base conventionally has a bayonet-type mount, in which protrusions of the base of the fluorescent lamp are fitted to recesses of a lamp holder and the base of the lamp is rotated with respect to the lamp holder, so that the protrusions of the base of the lamp are engaged with hooks of the lamp holder.
A conventional bayonet-type lamp holder and a base of a lamp are described with reference to FIGS. 18A, 18B, 19A and 19B. FIGS. 18A and 18B show a configuration of a conventional lamp holder 100. FIGS. 19A and 19B show a configuration of a conventional base of a lamp.
As can be seen from figures, the lamp holder 100 has a circular recess 101 formed at substantially center portion of a first mounting face 100a and four projections 104 formed at side faces thereof for projecting outward. The base 102 has a cylindrical protrusion 103 formed at substantially center of a second mounting face 102a and four engaging protrusions 106 formed at periphery portions of the second mounting face 102a for protruding upward. The cylindrical protrusion 103 of the base 102 is inserted into the circular recess 101 of the lamp holder 100. Each engaging protrusion 106 of the base 102 has an engaging groove 105 with which the projections 104 of the lamp holder 100 is engaged.
The lamp holder 100 further has a pair of hooking recesses 107, and the base 102 has a pair of hooking protrusions 108 to be hooked with the hooking recesses 107. The hooking protrusions 108 are formed on spring portions 109 which are formed on the second mounting face 102a of the base 102 and elastically deformed. The spring portions 109 are normally formed of a resin material integrally with the base 102.
The lamp holder 100 still further has two pairs of jack holes 110 and a pair of protrusions 112 formed on an inner face of the circular recess 101 and used for distinguishing wattage of the lamp. The base 102 still further has two pairs of pins 111 to be contacted with lamp terminals disposed below the jack holes 110 and a pair of grooves 113 formed on an outer face of the cylindrical protrusion 103 and engaged with the protrusions 112.
For coupling the base 102 with the lamp holder 100, the base 102 is placed to face the lamp holder 100 in a manner so that the second mounting face 102a of the base 102 contacts the first mounting face 100a of the lamp holder 100 and the cylindrical protrusion 103 of the base 102 is inserted into the circular recess 101 of the lamp holder 100, but the engaging protrusions 106 of the base 102 do not interfere with the projections 104 of the lamp holder 100. Under such a state, when the lamp with the base 102 is turned in a first turning direction around a center axis of the cylindrical protrusion 103 or the circular recess 101, the engaging grooves 105 of the engaging protrusions 106 of the base 102 are engaged with the projections 104 of the lamp holder 100. Dismounting of the base 102 from the lamp holder 100 due to turning in a second turning direction opposite to the first turning direction is prevented owing to the hooking of the hooking protrusions 108 with the hooking recesses 107.
In Publication gazette of Japanese Patent Application 2001-93631, an elastic hooking protrusion is formed on each groove 105 of the engaging protrusion 106 of the base 102 to be hooked with the projection 104 of the lamp holder 100, instead of the hooking recesses 107, the hooking protrusions 108 and the spring portions 109.
In the above-mentioned conventional bayonet-type lamp holder and the base of the lamp, in order to improve click feeling when the base of the lamp is mounted on or dismounted from the lamp holder, it is proposed to increase the elastic reaction force of the spring portion 109 or the elastic hooking protrusion. It, however, becomes easily be broken due to increasing of stress in the spring portion 109 or the elastic hooking protrusion. Furthermore, the resin material of the lamp holder 100 and the base 102 will be deteriorated while they are used in long term under high temperature condition. If the hooking protrusion 108 is broken due to the above-mentioned reason, the base 102 of the lamp is held on the lamp holder 100 only owing to the friction between the pins 111 and the lamp terminals. Since various vibrations including micro-vibration are applied to the lamp holder 100 and the base 102 of the lamp while the long use, the base 102 of the lamp is gradually loosened with respect to the lamp holder 100, and there is a possibility that the lamp falls to.
Furthermore, even if the base 102 of the lamp was engaged betwixt and between with the lamp holder 100, the lamp could be held on the lamp holder 100. Then, there was a possibility that the lamp fell to due to vibration or the like while the mounting of the lamp or while the use of the lamp.
Since the size of the lamp with a single base is upsized in recent years, the falling of the lamp is serious problem.